1. Field of the Invention
The invention relates to a planar product in which at least two fibrous plies are bonded to each other by a special adhesive agent, to the use of the adhesive agent for producing ply bonding of the fibrous plies and to a method of attaching at least two plies with each other. The present invention relates more particularly to tissue products, paper products and nonwoven products in which bonding of the at least two plies is achieved by said adhesive agent.
2. Prior Art
Tissue-making counts as a method of paper making, due to its basic agreement in the methods of production (wet-laying). Tissue making, better, raw tissue production—where involving the single-ply (intermediate) product produced on a special paper-making machine for the production of tissue or tissue paper—is characterized by its extremely low basis weight, usually less than 65, more preferably less than 45 g/m2 and its very high tensile energy absorption index. The tensile energy absorption index materializes from the tensile energy absorption by relating the tensile energy absorption index to the test specimen volume prior to testing (length, width, thickness of the specimen between clamps prior to tensile loading).
The high tensile energy absorption index of a tissue paper results from the outer and/or inner crepe. The former is produced by compression of the web of tissue paper adhering to the drying cylinder by the effect of a crepe knife, the latter by the difference in speed between two fabrics in sequence or, for example, between a sheeting fabric and one or two fabrics.
It is from this high tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5) that the majority of the useful properties usual for tissue and tissue products result. One example is tissue products for hygiene applications (hygiene products, more particularly hygiene paper products) which find application in a wealth of cleaning functions, e.g. in personal grooming and hygiene, in home, industry and institutional areas. They are used to absorb fluids, for decorative purposes, for packaging or even just as supporting material, as is common for example in medical practices or in hospitals. Hygiene paper products with their broad range of applications count today as products for everyday use.
“Tissue papers” or better, raw tissue papers are generally described as the single-ply intermediate products coming from the paper-making machine of lightweight papers, i.e. paper having low basis weight which as a rule is dry-creped on a yankee cylinder with the aid of a crepe knife, whereby the single-ply raw tissue may be built up of one or more layers. “Tissue products” are single or multi-ply finished products produced from raw tissue tailored to final consumer requirements, i.e. tailored in accordance with a requirements profile differing in many respects.
Typical properties of tissue products are their good ability to absorb tensile stress, their draping facility, good textile-like flexibility—properties often termed bulk softness—high surface softness, high specific bulk coupled with a perceptible thickness, an as high as possible liquid absorbency and depending on the application a suitably good wet and dry strength whilst featuring an interesting visual finish of the outer product surface. It is due to these properties that tissue papers are worked into tissue products (tissue paper products) available to final consumers in a wealth of different types and tailored applications, for example as wipes, towels, household and especially kitchen towels, as sanitary products (e.g. toilet papers), paper handkerchiefs, cosmetic tissues (facials) serviettes/napkins or medical garments.
Softness is an important property of tissue products such as handkerchiefs, cosmetic wipes, toilet paper, serviettes/napkins, not to mention hand or kitchen towels, and it describes a characteristic tactile sensation caused by the tissue product upon contact with the skin.
In simplified terms, softness can be subdivided into its main characteristics, surface softness and bulk softness. Surface softness describes the feeling perceived when e.g. one's fingertips move lightly over the surface of the sheet of tissue. Bulk softness is defined as the sensory impression of the resistance to mechanical deformation that is produced by a tissue or tissue product manually deformed by crumpling or folding and/or by compression during the process of deformation.
Where multi-ply tissue products are concerned, care must be taken that the individual plies are bonded to each other by adequate ply bonding, although the ply bonding should not have a negative effect on the softness and absorptivity. Producing ply bonding by mechanical embossing pressure is disclosed for example in GB-C-363699. However, the ply bonding produced thereby is not particularly strong. Apart from this, the necessary high embossing pressure may result in embossing knobs (protrusions) in the finished product which are conspicuous and rough to touch.
This is why ply bonding by chemical methods, i.e. gluing has materialized. Making use of an adhesive in this respect also in combination with mechanical techniques (embossing methods) has found application in producing ply bonding. U.S. Pat. No. 3,673,060 and U.S. Pat. No. 5,173,351 teach, for example, applying an adhesive in the region of the embossing roll directly to the side of the paper web to be later located on the inside of the multi-ply product.
The adhesives employed for a chemically produced ply bonding typically contain components soluble or dispersible in water such as polyvinyl alcohol (see also U.S. Pat. No. 3,673,060), polyvinyl acetate, carboxymethyl cellulose, starch etc.
Conventional adhesives have the disadvantage, however, of losing their adhesiveness when wet and the individual plies become detached from each other when the tissue paper is used when wet. The technical problem involved in this respect is the subject-matter of WO 97/11226. This publication teaches the addition of a water-soluble cationic polymer (glyoxalated polyacrylamide, polyethyleneimine and preferably polyamide epichlorohydrine resin) to an adhesive on the basis of conventional adhesive components (starch, polyvinyl alcohol) to enhance the bonding capacity of the adhesive when wet.
The technique described therein for improving the ply bonding in multi-ply paper, more particularly in tissue products, does not always result in satisfactory ply bonding when dry and/or wet.
Problems associated with ply bonding when dry and/or wet may also be encountered in other planar products having a plurality of fibrous plies (more particularly cellulose fibrous plies) such as non-woven or textile plies.
A further problem arises if two or more plies of a multi-ply product shall be attached to each other and if these plies comprise lotions or other components which were added e.g. to improve the softness of the multi-ply products and which might inhibit or prevent the ply-attachment. Lotions often times comprise compounds which will prevent a suitable ply-attachment.
Therefore, there is a need to provide an adhesive agent which is capable of providing a suitable ply attachment between two plies of a product, especially between two plies of a product which comprises lotion or other ingredients which can inhibit a conventional ply-attachment. Another problem arising when conventional adhesive agents are employed is their non-compatibility with the present demands on easy and quick degradation in landfills. Therefore, there is also a need for adhesive agents for use in multi-ply products, which are oftentimes disposable products, which are easily degradable in landfills and which do not strain or pollute the environment.